Measures of central tendency and measures of dispersion

Abstract

The previous two chapters looked at ways of describing data in tabular and graphical form. These forms of describing data give some sense of the overall distribution of cases. However, we sometimes want to capture something a little more specific about the data: what does the ‘typical’ or ‘average’ case look like? Similarly, we might ask how much variety or similarity there is among the cases. For example, we might know that the average score in an exam is 65, and that all the scores lie between a minimum of 24 and a maximum of 87. The first of these numbers (65) — which represents the ‘average’ or ‘typical’ score — is called a measure of central tendency. The second set — which indicates the spread of cases across the values of the variable — is called a measure of dispersion.